Document qmExN814GayD645obywqqeNaK

scf-fa-iwo Asbestos Content of Dust Encountered in Brake Maintenance and Repair by A N Rohl PhD. A M Longer PhD. R Klimentidis ba. M S WoUT PhD and I J SelikotTMD [Environmental Sciences Laboratory, Mount Sinai School of Medicine of the Citv University of Sew York. Sew York. AT 10029)' Asbestos in Brake Linings The composition of automotive brake linings in cludes chrysotile asbestos fibre which comprises about 50D of the friction material. The exposure of garage workers to asbestos during brake lining maintenance and repair has recently been in vestigated (Rohl et at. 1976). This important issue was studied because a large labour force is poten tially exposed (over one million people in the United States alone). Consequently it was thought essential to determine if chrysolite fibre survives braking, and to measure the amounts liberated as an aerosol during maintenance and repair oper ations. Investigators in the past have expressed doubt as to whether chrysotile fibres can survive the high temperatures generated during braking (Lvnch 1968. Hickish & Knight 1970. Hatch 1970). Chry sotile is alleged to be subjected to temperatures in excess of 800C. which would cause its thermal transformation to forsterite or to an amorphous magnesium silicate phase. While 'hot spots' up to 1000C may be attained (Carroll 1962), the heat distribution is nonuniform, and other processes, in addition to thermal wear, contribute to de gradation of brake linings. For example, abrasion and macroshear may also cause physical break down (Burwell 1957, Mizutani et at. 1973). Ac cordingly. brake lining disintegration by these mechanisms may liberate partially altered or even unaltered chrysotile fibres. Analysis of Brake Drum Dust Initially, (en samples of automobile brake drum dusts from b.rake-repair shops in New York City were collected and examined by optical micros copy. X-ray diffraction, transmission electron mic roscopy and energy dispersive X-ray spectroscopy, to determine the presence of chrysotile. Optical microscopy: The detection of chrysotile in brake drum dust by optical microscopy is hindered by the nature of the debris matrix, consisting largely of opaque pyrolvzed phenolic-type resin binders and road dust. Chrysotile. particularly small fibres, has low optical relief and low' birefrin gence. which further hinder its identification. Onlyin rare instances have large fibres, with optical 8001 0015 punrii irnn nv popn Section ^ Jccupationai Medicine Table i Chrywtik ftitMSios content of brake drum dints Great Britain West Germany Franc* Unued States of America Finland Western Australia Xv. ot samples 8 tt \ X-ray diffraction {step-scam ....-................. ' : ; Xu. positive MV/yAr percent Mean kontff 6* 1.8 0.7-2.3 5* 2.4 0.5-3.2 l 2.5 10 10 53 7J J.5 2.0-15.1 1.8 U.8-2.5 J.4 0.5-5.3 39 29 r II I simple possibly positive Transmission electron niteroscupv Xn. pft.Mtirc 8 8 1 to < 7 39 properties consistent with chrysotile. been obser ved with this technique. X-ray dijjractometry: The ten brake dust samples were analysed by X-ray diffractometry, in both continuous and step-scan mode. The diagnostic reflection selected for chrysotile (3.66 A; hkl~ (004)) was step-scanned in the fixed-count mode. By comparison with external standards, the amount of chrysotile present can be determined. Chrysotile reflections were observed in all samples, with weight percentages estimated to range from 2 to 15 (average 4.5). Lead compounds, quartz, carbonate minerals, clays, halite (NaCl). graphite, micas and alpha-iron were also identified in vari ous samples. Twenty-nine additional brake drum dust samp les were collected by colleagues in four European countries and Australia. The samples were ob tained from areas representing variable circum stances. such as driving conditions, friction material composition, type of automobile and climate. The results of X-ray diffraction analyses are presented in Table 1. Of the 39 total samples analysed (including 10 United States samples) chrysotile was found in 29, or about three-fourths. The mean chrysotile content varied from 1.4*;, in the seven Australian samples to 4.5 "c in the New York City samples. The thermal breakdown product of chrysotile. i.e.. forsterite. which might be expected to form as a result of reervstalibation, was not unambigu ously detected in any sample. 7ransmission electron microscopy (TEST): In order to verify the results of X-ray diffraction analysis, the brake dust samples were prepared for electron microscopic analysis by means of a technique which disperses the dust particles in a nitrocel lulose film without altering particle sbes. Both free chrysotile fibre bundles and fibrils were observed in all 39 samples. Most of the chrysotile retained its characteristic morphology without significant alteration, and selected area electron diffraction patterns obtained on representative fibres dem onstrated the preservation of crystal structure as well (Fig 1). Fibre size distribution: In ten brake dusts sampled in New York City, free asbestos fibres were sbed by TEM at magnification 42 000. The results showed that about 80 "0 ofchrysotile is in free fibril form and is shorter than 0.4 pm in length. Over 57% have lengths of about 0.2 pm. At magnifi cation 40 000, such a fibre would be about I cm long. If lower magnification were used to scan for asbestos, significant numbers of fibres might not be detected. It is obvious that most fibres are too small to be seen by optical microscopy. The Asbestos Stan dard adopted by the Occupational Safety and Health Administration (OSHA) of the US Depart ment of Labour is limited to optica) microscopy and neglects to count or control fibres less than 5 pm long. On the other hand, accumulating evidence suggests that such small asbestos fibres may produce disease (Holt et al. 1964. Davis 1965. Pott et al. 1972. Wagner et al. 1973. Hilscher et al. 1970. Bouhuys 1975). ' Air sampling: Eight personal air samples taken during brake repair work were selected for electron microscopic analysis. This was done in order to positively identify chrysotile in the samples and to determine whether a systematic relationship existed between optically and subnticroscopically visible fibres for this type of exposure. The memb rane fillers were ashed in plasma oxygen to elimin ate organic materials and the residue was prepared for electron microscopy by a 'rubout' technique (Nicholson et al. 1971). which comminutes large chrysotile fibre bundles into individual fibres and fibrils. Large inorganic particles are likewise re duced in size, permitting all chrysotile to be seen and measured. Chrysotile was identified in the eight samples, in both fibre and fibril form (Fig 2). By measuring a large number of fibres at magnifi cation 42 000 and converting the volumetric data into mass, a concentration per volume of 3ir is determined. Comparison of optical microscopic 60DJ 0016 PROTYl 'rPTT PY FOPT) 34 Proc. rov. Soc. Med. Volume 70 January I97i fibre counts and the electron microscopic asbestos mass calculations indicates that a positive cor relation exists between the two sets of data. These results show that the standard (OSHA) optical fibre counts may be only indicative of the total asbestos exposure. Asbestos Exposure of Workmen After the identification of chrysoiile in the brake drum dusts, asbestos fibre exposure during main tenance and repair was determined by personal air sampling carried out at automobile repair shops. taxi fleet repair shops and a municipal truck repair shop in New York City. Air sampling and analyti cal methods for the determination of fibre con centrations were in accordance with the OSHA techniques (Bayer et ul. 1975). Present regulations of OSHA prohibit asbestos concentrations of 5 fibres per millilitre (fiml) or greater, longer than 5 pm as a time-weighted average, and con centrations above 2 f.'ml will be illegal after July 1976. Peak concentrations or maximum excursions of 10 (7ml are permitted by the regulations. In brake lining inspection and repair, the wheel Fie I Electron photomierooraphs ot broke drum Justs, token ot carious magnifications. a. the numerous chrysolite fibrils hove overage lenotiis ot O.J uni or less l x JO OVID. B. large numbers ot'ehrysotile fibres imbedded in. omi protruding from. opauue particle. probable pyrouzed piicnolic resin hinder i * SO UOt)). c. larue chrysolite fibre bundle 4 * tjVd). D. taroe particle tn left centre oj photograph is the same us in c. but cannot be identified at low niaynifu otion \ * fJtJt)\ 6001 0017 PRODUCED PY FORD Section of Occupational Medicine 35 is removed from the axle and loose dust is com monly removed from the drum and back plates by means of a jet of compressed air. A survey of 220 garages in Baltimore and Washington. DC has shown that this is the method of choice in 80% of the shops (Castleman et at. 1975). A similar situation exists in New York City. The data in Table 2 show that fibre concentrations are high in the breathing zone of the operator during com pressed air blowing. An asbestos concentration gradient, diminishing with time and distance away from the operation, appears to occur. Persons up to 22 m from such activity are exposed to measur able concentrations of asbestos. Personal air sampling was also conducted at New York'City Department of Sanitation where truck brakes are repaired. Used linings are salvaged by machine grinding to remove dirt and grease from the surface. New linings are bevelled by grinding to reduce noise and improve break-in. Accordingly, these studies relate to levels of as bestos exposure which may be experienced by workers engaged in brake lining manufacturing. Table 2 shows that fibre concentrations experi enced during grinding ranged from 1.7 to 7.0 f.ml of air in the breathing zone of the operator. The background or area samples for this operation ranged from 1.2 to 0.2 f/ml. with a general decrease Fic 2 Electron photomicrograph.1 of personal air samples taken during broke repair work. Clumps of chrysolite are' associated with opaque panicles oj road dust and resin binders, a. b. x 6U 000. C. D. x ,"2 001) 8001 0018 T>T>rvm tr'Trr> v 36 Proc. roy. Soc. Med. Volume 70 January 1977 Table3 PefiCfil sir s*m>MIc tad truck krskt r*glr Automobile brake repair Blowing dust from brake drums: Distance 1-1.5 m Distance 1.5-3 m Distance 3-6 m Background (5 min after air jet blowing, distance 3.6- 16 mi Background (7-14 mm after air jet blowing, distance 19.6-22.6 mi Peak fibre concentration So. of [fibres per mf) samples Mean Ronge J IS.O *3 3.3 1.6 2 o.: % 0.1 6.6-29.4 2.B-4.2 0.3-4.8 o.i-o.: 0.1 13 Truck broke repair Renewing used linings by grinding (distance 1-1.5 m) Background to grinding used linings: Distance 3.3 m Distance 8.3 m Distance 20.0 m Bevelling new linings Background to bevelling new linings: Distance 2.4 m " Distance 3.6 m Distance 9.] m 10 > T 4 1 * I 4.8 I.J 0.8 37.3 0.4 1.7-7.0 i.:-i.7 0.6-1.0 0.2 23.7-::.o 0.6 03-0.5 0.3 23 away from the operator. From six to ten other mechanics work within an area up to 20 m from this operation are exposed to asbestos as well. Since a person breathes about one cubic metre of air an hour, multiplication of the fibre con centrations by one million gives the number of fibres inhaled during this period. Fibre con centrations measured during bevelling of truck linings were as high 8S 72 f/ml and averaged about 37 f/ml. Background counts were measured up to 9.1 m away from this operation (0.3 f/'ml'). Fibre concentrations measured during drilling holes for rivets and grinding ranged from 0.3 to 29.2 f,'ml. as reported by Boillat & Lob (1973). Four of the nine values exceeded 5 f/ml. Conclusions The existence of significant exposure during brake servicing operations necessitates the following measures: ledge support under a grant from the National Institute of Environmental Health Sciences. ES 00928 and support bv the Ford MotorTjctmpanv. MSW wishes to acknowledge support unde: a post-doctoral fellowship from the N1EHS. ES 02565. We are grateful to the following for assistance ir. obtaining brake dust samples: Professor Donald Bowes. University of Glasgow. Scotland; Mr L B Bowes. Department of Labour and Industry. Adel aide. Squth_Australia: Dr Trevor Turner. Adel aide. Sputh_Australia; Professor Jean Bignon. Hospital Laennec. pads^France: Maunu Harme. Geological Survey of Finland. Otanienti. Finland: Dr G. Gaal. Helsinki University of Technology. Helsinki. Einlaod; Dr K. Robock and Dr W Klosterkotter, Institut fur Hygiene und Arbcitsnte- dizin des Klinikum der Universttat Essen. West Germany. (I) Implementation of industrial hygiene pro- ced.ur.esjo control exposure. * (2^ Clinical studieS~~Of garage mechanics to de termine evidence of asbestos-related disease. i.3> Epidemiological studies of the mortality ex perience of exposed workers. ' In addition, the entire variety of dusts and other materials present in brake repair work should be characterized in order to determine its disease potential, especially silica and lead compounds. Acknowledgment: The authors wish to acknow REFERENCES Bayer S C. Browo T A St 2.umakk R D (197$) Document TR-&4. US Public Health Service. Cincinnati. Ohio Boillat M A it Lob M (19*3) Bouhuya A medizinische Wochenschnit 103. 39 {19*5) Annuls of Internal Medicine 83. 898 Harwell J T 11957) H ear J. 119 CirTolt W C i m:)BruLtbPlauics 3S.-H4 Cattleman B. Camarota L A. Frilaeh A J. Mauocchi S 4 Crawley ft C 119*5) Public Health Reports 90. 254 Darn J M J (1965) Annols oj the Sew York Academy ofSciences 132. 98 6001 0019 pprvrvt tpT?n Ttv prvpri Hatch D (1970) Annals of Occupational Hygiene 13. 25 Hlckisb D E A Knight K L (1970) Annals ofOccupational Hygiene 13. 17 Hlbcher W. Sethi S. Friedrichs K H A Port F (1970) Naturwissenschaj'ten j?. j56 Holt P F. 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